You have anger issues and insecurities. The most efficient way to deal with these issues is to consult a therapist. If therapy is not an option, then you may want to consult self-help books or materials.
Having anger issues and insecurities may explain why you repeatedly find yourself in unhealthy relationships and it may effectively explain your current behavior. You are engaging in the very behavior that has hurt you in past relationships. Cheating not only destroys relationships, it is emotionally and psychologically damaging to your partner. It is never okay to hurt someone you care about. A more effective approach would have been to have a discussion with your partner. If that did not decrease your fears, then consulting a therapist or an outside objective party would have been in order.
What you cannot do is to allow the pattern of cheating and self-sabotage to continue. I would highly recommend seeing a therapist for your ongoing relationship issues. You are having difficulty sustaining healthy relationships. Your behavior in your current relationship is self-sabotaging. It is not healthy. It hurts you and your partner, it has seriously damaged this relationship and if is not corrected it will damage future relationships. You should not continue on this path. It is important that you correct these issues. Click the find help tab at the top of this page to help you locate a therapist. I wish you well. Please take care.